Atom 32K SRAM expansion

[TheCorfiot]

Hello chaps..

This one is mainly for our dutch friends, roland and kees.

I am looking at using a 32K 62256 SRAM chip to populate the Atom memory map from #0000 to #7FFF.

Although the interfacing is quite straight forward my options are to etch a pcb or wirewrap a working prototype, when I found this.

http://www.acornatom.nl/hardware/cmos/cmos.html

And I am wondering if any of these pcbs exist in Holland, either completed, bare, or even broken,as it would make life easier...

If I were to map the full lower 32k ram using a single chip, would I expect problems using a disc pack... I believe the 3k in the disk pack can be removed but would the 32k sram clash with the 8271 IO memory mapping.

On another note, do you guys have a mod to the reset circuit as I notice my Atom never needs Break to be pressed at power up it always starts perfectly, however I think it maybe causing issues with the interrupt generation needed for the #A000 firmward for Charlue's MMC.

If such a mod does exist can someone pls tell me what it is so I can check if my board has been modified.

Cheers guys
TC

[Prime]

If you can wait 2-3 weeks I have a new batch of Atom RAM/ROM / Clockboost boards on order.

This will give you the 32K of RAM plus the option of running the processor at 1.7MHz, which as well as being faster, as the CPU is synced with the 6847, you don't get interference when writing to the video RAM.

Cheers.

Phill.

[TheCorfiot]

Phill
That would be my ultimate solution my friend but I am skint, boohoo.
How much do they cost please...

TC

[roland]

Hello TC,

Phill's board sounds very attractive but if you're blunt you'll have to find other ways to get 32k. I don't have such an memory pcb, but if you can create a memory card by mounting a 62256 on a vero board and place the long pens into the sockets of 2114 and the decoding ic's in the area of ic 5, 6, 7 etc. It can work out but you have to puzzle a bit to get it fitting. But that's what the Atom was made for

If you have 32k lower memory you have to make one of these modifications:
- move the FDC I/O to #BC48 like we modded the FDC card and DOSROM
- disable the 62256 when #0Axx is addressed

But let us wait on Phill's answer about the costs of his ram/rom boards. If you decide to buy one, all "problems" are solved, otherwise I have a bare combicard with

- 32 kb rom at #C000 - #FFFF (bank switching os rom space, e.g. Atom and BBC Basic mosrom)
- 8 * 4 KB rom at #A000 - #AFFF
- 8 * 4 kb ram at #A000 - #AFFF
- 32 kb ram at #0000 - #7FFF

The card is mounted on PL6/7 and needs some (reversible) modifications on the Atom main board. If you're interested in this card including an eprom and two or three 32k ram chips, just PM me as not everybody needs to know you can have it for free

Regards,
Roland


The left card is my card, being modified at the moment. The card on the right is a bare pcb, even the holes aren't drilled yet....

[oss003]

And I am wondering if any of these pcbs exist in Holland, either completed, bare, or even broken,as it would make life easier...

Hi TC,

I've never seen one but that doesn't mean nobody had installed one.

The easiest way is to take a pcb, get A0-A9 from the 2114's and A10-A14 from IC6. Use A15 from IC6 for CS signal. OE should be connected to GND and WE to NWDS.

Problem is the 8271 at #0A00 if you're using Atom DOS or patch the DOS controller board to use another address.

Greetings
Kees

[TheCorfiot]

Thanks for the replies and offers guys....

I now fully understand your reasons for modding the atom disc packs to use the alternative higher io address mapping.

As it stands, I have ram from #2000 to #7FFF and the 1k zero page, I am just missing the 7k in between..if I wire even a 6264 8k sram to fill #0000 to #19FF then this upsets the disc pack, I cant switch it out either as I will then lose zero page ram....doh

I wonder if Phill's Ram / Rom board can be setup to function with the disc pack, ie selecting Atom DOS as the #E000 rom also creates the #A00 window... but selecting the MMC rom at #E000 will then provide full 32k lower ram with no gaps...

Roland thank you for the very kind offer, I will await Phill's response before I take you up on the board offer..would be a better solution than just my sram as I will then be able to fit pcharme, gags and other utility roms at the same time..

But yes these are fantastic machines for hardware mods indeed.

Any comments on my Break behaviour mentioned above?

Thx guys

[danielj]

I wonder if Phill's Ram / Rom board can be setup to function with the disc pack, ie selecting Atom DOS as the #E000 rom also creates the #A00 window... but selecting the MMC rom at #E000 will then provide full 32k lower ram with no gaps...

Indeed it can! Have a peek in here: http://www.stardot.org.uk/forums/viewto ... tom#p72918

Currently mine is set by default to allow the disc pack to work, but a ?#BFFE=6 brings the ATOMMMC to life and puts the disc pack to sleep (DiscRomEn is disconnected on Phill's board)

d.

[roland]

Any comments on my Break behaviour mentioned above?

There is a mod for the reset circuit, using a TL7705. Take a look at the diagram on http://acornatom.nl/atom_nieuws/1988/nr1/19881075.htm

But as I remember, your Atom doesn't have such a mod. Some Atoms simply donwhat they have to do, even when waking up. Mine doen't but I don't care...

[TheCorfiot]

Cheers roland, my beautiful atom does not have that mod, may scope the interrupt and reset lines to see what is going onregarding the atommc.

Daniel, Phil's board sounds the one for me really,, but ow much lol.

TC

[1024MAK]

You could always build some logic to disable the SRAM in the memory range used by the disk pack.

Mark

[CMcDougall]

my Atom never needs Break to be pressed at power up it always starts perfectly

join the club, only about 5% of the time I get no "ATOM" at power up, but a press of break, and she's back

but How much lol

an old thread says £35+PP, but demand has grown rapidly, so price will go up! (well, that's what economics taught me )

[oss003]

Hi guys,

it's not a 100% guarantee but you could try to solder a capacitor parallel on C11 to delay the reset. You can experiment with values but a 10 uF ELCO worked for mine Atom.

Greetings
Kees

[TheCorfiot]

Kees my friend

She is beautiful, congrats..

I have the opposite issue regardinng reset.
Mine always boots perfect. Just wondering if it's causing issues with the interrupt generation from the atommc interface as I have to break a. Good few times for the card to initialise, using A000 rom and lk3 made....

Cheers
TC

[oss003]

Kees my friend

She is beautiful, congrats..

I have the opposite issue regardinng reset.
Mine always boots perfect. Just wondering if it's causing issues with the interrupt generation from the atommc interface as I have to break a. Good few times for the card to initialise, using A000 rom and lk3 made....

Cheers
TC

Hi TC,

AtoMMC at #Axxx is not so stable due to bouncing reset pulses. I have looked at it if I could eliminate these pulses but I didn't succeed. The idea was to use a Smitt-Trigger IC instead of the 74LS04 in the BREAK circuit.

The best way is to use the AtoMMC at #Exxx with a kernal patch at #Fxxx. This always works 100%.

Greetings
Kees

[Prime]

Cheers roland, my beautiful atom does not have that mod, may scope the interrupt and reset lines to see what is going onregarding the atommc.

Daniel, Phil's board sounds the one for me really,, but ow much lol.

Sorry I could have sworn I had replied to this, but now I look it's not there I guess I must have forgotten to click 'submit'.

Anyway last time I did them for £35 + p&p built, assuming component prices have not changed much I would do the same again.

Cheers.

Phill.

[TheCorfiot]

Phill

Pls put me down for one definitely.

@kees
I had a feeling it was down to the break upsetting the #A000 firmware.
I plan to move onto Phill's board when they are available so I will then use the #E000 firmware, give SDDOS a whirl too...But I would like to keep my disc pack operational too.
Jason watton has been in touch, author of omniflop and I hope to help him implement full Atom disk writing support....

Exciting Times for the Atom indeed, who would have thought the popularity would rise again to such a level so quickly.
I'm without doubt we have to thank our Dutch friends for their kindness in sending and keeping those systems within our community.
HipHip

TC

[CMcDougall]

the atommc interface as I have to break a. Good few times for the card to initialise, using A000 rom and lk3 made.

ahh, so again, also in the same club as me

AtoMMC at #Axxx is not so stable due to bouncing reset pulses. The best way is to use the AtoMMC at #Exxx with a kernal patch at #Fxxx. This always works 100%

so, sending mine to Charlie was a complete waste of time, as he said the other day it's 100% fine
....so won't have to re-flow all the solder joints now! (was next mission) ..waits for postman to return card, and press break more times!

[TheCorfiot]

Hey Col,

Power on always initialises the AtomMMC fine as does issuing the Link#AFCC statement.

TC

[CMcDougall]

Power on always initialises the AtomMMC fine as does issuing the Link#AFCC statement

remembers NOT to press Break, always full reset

without doubt we have to thank our Dutch friends for their kindness in sending and keeping those systems within our community.
HipHip

seconded! Horay! , I think Roland is God of the year in my book,
I even think Santa is not real now , as he brought something magic months early!

[oss003]

Hey Col,

Power on always initialises the AtomMMC fine as does issuing the Link#AFCC statement.

TC

Yep, power on does a reset with one reset puls, BREAK does a reset with bouncing pulses, that's the difference.

Who ... Roland-a-Claus ..

Greetings
Kees

[roland]

without doubt we have to thank our Dutch friends for their kindness in sending and keeping those systems within our community.
HipHip

seconded! Horay! , I think Roland is God of the year in my book,
I even think Santa is not real now , as he brought something magic months early!

Who ... Roland-a-Claus ..

Guys, you make me breathless and blushing

But I really appreciate your thankfulness.

[TheCorfiot]

Roland, you are indeed a genuine top guy..
If ever you visit South Wales, you have a place to stay with plenty of drink, food and Acorns to consume....

I mean it....
TC

[TheCorfiot]

Kees,

Out of curiosity,
Why must I use the NWDS for the SRAM WE line.
Can I not directly use R/W from the 6502.

thx buddy

[oss003]

Kees,

Out of curiosity,
Why must I use the NWDS for the SRAM WE line.
Can I not directly use R/W from the 6502.

thx buddy

Hi TC,

R/W has to be synchronized with PHI2 that's what the NRDS and NDWS signals are.

Greetings
Kees

[TheCorfiot]

Kees,

Out of curiosity,
Why must I use the NWDS for the SRAM WE line.
Can I not directly use R/W from the 6502.

thx buddy

Hi TC,

R/W has to be synchronized with PHI2 that's what the NRDS and NDWS signals are.

Greetings
Kees

Which makes perfect sense..yet the 6522 is driven by R/W and the dutch design linked to above also uses R/W from the 6502 for the 32k sram...

Just trying to understand this all a bit better...

Thx

[roland]

Hi TC,

Using R/W or NRDS/NWDS depends on the chip being read from or written to. Intel chips do often have seperate inputs for reading and writing, take a look at the 8255. The intel processors have separated output for read and write. So in this family of cpu and peripherals you can connect the reads and writes directly to each ofther.

The 6502 and 6522 are also from the same family, so you can connect the R/W pins to each other.

When accessing memory, it depends on the chip. A Samsung KM62256 for example, has two write modes. See http://pdf.datasheetcatalog.com/datashe ... 283_DS.pdf
You can use both CS and WE to end a write cycle. In short, a write occurs during the overlap of a low CS and a low WE. A write begins as both CS and WE are low. A write ends if one of them is going high with the restriction that if WE goes high before CS that CS has to stay low for that minumum time.

But like Kees wrote, by synchronizing with phi2 you always have proper setup and retention times for non-65xx chips. So that is the safest way.

Greetings,
Roland

[Prime]

Hi TC,

Using R/W or NRDS/NWDS depends on the chip being read from or written to. Intel chips do often have seperate inputs for reading and writing, take a look at the 8255. The intel processors have separated output for read and write. So in this family of cpu and peripherals you can connect the reads and writes directly to each ofther.

The 6502 and 6522 are also from the same family, so you can connect the R/W pins to each other.

The 6522 also has an input for phi2 so I guess it generates the strobes internally as needed. This is also true for 68xx chips as they use essentially the same bus except use the E clock instead of phi2, not surprising as the 65xx series where designed by the same team that designed the 6800

So if you want to use a 6821 for example on a 65xx connect phi2 to E and R/W to R/W and likewise the other way round.

Incidentally one of the things the CPLD on the RAMROM board does is the generation of the /WE and /OE for the RAM and ROM chips.

Code: Select all

	// Generate Intel type RD and WR strobes for ROM and RAM 
	assign RDS	= (PHI2 & RW);
	assign WDS	= (PHI2 & ~RW);
	
	assign NRDS	= ~RDS;
	assign NWDS	= ~WDS;

Cheers.

Phill.

[TheCorfiot]

Thanks for the response guys, it's all loud and clear....

I built my little sram board before reading this thread so I used the R/W line direct from the CPU..
It's basically a liitle piggyback board that plugs straight into the 6502 with pass through pins and a 62256 SRAM..measures 2.5" by 2".
It's all handwired under the board using 28 guage kynar so its all quite compact.

And it works great, passes full RAM tests from #400 to #7FFF and the Atom is stable.
I removed All lower text RAM and have not connected the disc pack as I know it will clash at #A00

It's running Atommc perfectly and have enjoyed playing Galaforce and Chuckie Egg at last.

I wont mod the Disc Pack as I will eventually replace this with one of Phill's RomRam boards as soon as they are available.
But as a temp solution, I am over the moon with it..

Thanks all for your support and help with this Chaps...

TC

[roland]

Hey TC,

You forgot to attach a photo

Regards,
Roland

[TheCorfiot]

Hey TC,

You forgot to attach a photo

Regards,
Roland

Will upload tomorrow